Endovascular delivery catheter assemblies are used to implant prosthetic devices, such as a prosthetic valve, at locations inside the body that are not readily accessible by surgery or where access without invasive surgery is desirable. For example, aortic, mitral, tricuspid, and/or pulmonary prosthetic valves can be delivered to a treatment site using minimally invasive surgical techniques.
An introducer sheath can be used to safely introduce a delivery apparatus into a patient's vasculature (e.g., the femoral artery). An introducer sheath generally has an elongated sleeve that is inserted into the vasculature and a housing that contains one or more sealing valves that allow a delivery apparatus to be placed in fluid communication with the vasculature with minimal blood loss. A conventional introducer sheath typically requires a tubular loader to be inserted through the seals in the housing to provide an unobstructed path through the housing.
Conventional methods of accessing a vessel, such as a femoral artery, prior to introducing the delivery system include dilating the vessel using multiple dilators or sheaths that progressively increase in diameter. This repeated insertion and vessel dilation can increase the amount of time the procedure takes, as well as the risk of damage to the vessel.
One solution has been the development of radially expanding introducer sheaths. For example, U.S. Pat. No. 8,790,387, which is entitled EXPANDABLE SHEATH FOR INTRODUCING AN ENDOVASCULAR DELIVERY DEVICE INTO A BODY and is incorporated herein by reference, discloses a sheath with a split outer polymeric tubular layer and an inner polymeric layer, for example in FIGS. 27A and 28. A portion of the inner polymeric layer extends through a gap created by the cut and can be compressed between the portions of the outer polymeric tubular layer. Upon expansion of the sheath, portions of the outer polymeric tubular layer have separated from one another, and the inner polymeric layer is expanded from a folded configuration into a substantially cylindrical tube. Advantageously, the sheath disclosed in the '387 patent can temporarily expand for passage of implantable devices and then return to its folded configuration and associated starting diameter.
Expandable introducer sheaths, however, have some challenges. One of these challenges is that expandable sheaths can increase the amount of force needed to advance the delivery apparatus—such as a delivery catheter having mounted on its end a stent-mounted prosthetic heart valve—to the deployment site. Push forces also need to be mediated in conventional introducer sheaths.
As a result, there is a need to address the push forces required for delivery of implants through introducer sheaths.